Respiratory activity is easily manipulated in yeast in contrast to mammalian cells. Therefore investigations of this cell system continues to provide important information about the biogenesis of mitochondria. However virtually nothing in known about mitochondrial messenger RNA and the regulation of its synthesis during mitochondrial biogenesis. I propose to provide this information by developing methods for titrating mitochondrial mRNA in S. cerevisiae undergoing a change in respiratory activity. These methods will provide a means of directly determining the extent to which control of mitochondrial mRNA synthesis contributes to the regulation of respiratory activity.